Slide projectors are increasingly used in technical devices for reproducing pictures or images on a projection surface of the projector which is visible from the outside. For example, an apparatus is known for coding medical findings and diagnoses which comprises a frosted glass plate within an image field onto which plate medical images may be projected for the purpose of automatic recording of the findings. An arrangement for coding predetermined data is disclosed in U.S. Pat. No. 3,775,560 which is provided with a display surface for feeding defined values into a data processing unit. It is also possible with this known arrangement to provide the display surface in the form of a projection screen onto which images or pictures are projected by means of a projector, which images then facilitate the feeding into the data processing unit.
In the above-mentioned cases it is necessary to exactly fix the projection position for the film slides, so that each projected image will deviate from its correct or ideal position within only very narrow tolerances in order to allow a trouble-free input of data into the data processing system. Moreover, the operation of the projector should involve as little noise as possible, and the individual slides should be advanced rapidly from the magazine into the projecting position and returned from the latter position to the magazine.